Computed radiography (e.g., as defined under ASTM Standard E2007; and ASTM Standard E2445) is a modality of planar x-ray imaging. The radiograph is recorded on a flexible sensor plate that contains a thin phosphor layer. The image is stored within the thin layer by the energy states of the electrons in the crystal lattice of the phosphor. A plate based on this mechanism is called a photostimulable phosphor plate. The image is converted from this analog format to a digital format using a computed radiographer reader. The reader is a confocal laser scanning device, called a read out unit, that interrogates the phosphor layer by a raster scan by a point-focused laser. The phosphor responds to the laser by emitting light with an intensity proportional to the density of the excited electrons. A photosensitive detector (e.g., photomultiplier) has its sensor aperture focused onto the same point as the laser. The detector senses the magnitude of the resulting fluorescence and electronically passes the intensity to an analog-to-digital converter that outputs the digital reading to a host-computer's peripheral input device. The digitized image is placed into a computer memory such as a standard hard disk or random access memory. The computer formats the scanned series of digital readings into a 2D image format with rows of pixels. Advantages of computed radiography compared to conventional film radiography (e.g., ASTM Standard E94) include an avoidance of the complexities, expense, risks and potential environmental hazards of chemical film processing.
Computed radiography is a different modality than digital radiography (e.g., ASTM Standard E2736). With digital radiography the sensor plate is directly attached to the computer that holds the images. The x-ray intensities are sensed by a pixelated solid-state digital detector, sometimes called a flat-panel sensor, that is electronically attached to the computer system.